I don't have the source to hand right now but I believe the last time I looked at the crime statistics for rape (in the UK) they roughly mirrored those of violent crimes, with a conviction rate of about 7% of reported crimes (that doesn't include situations where a rape was reported but the perpetrator was convicted of a different offence such as sexual assault and the like).

The "issue" (for lack of a better term) with rape is the reporting rate, which while hard to quantify is normally far below that of violent crimes.